SW6210202_RIPRAP E_20210406

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Designed By: Steve Waldron Date: 8/17/2020
Checked By: Ryan Jones Date: 8/17/2020
Company: LOWE ENGINEERS
Project Name: SOF OPERATIONS FACILITY
Project No.: 19-0049
Site Location (City/Town) FT. BRAGG
Culvert Id. E
Total Drainage Area (acres) 1.02
Step 1. Determine the tail -water depth from channel characteristics below the
pipe outlet for the design capacity of the pipe_ If the tailwater depth is less
than half the outlet pipe diameter, it is classified minimum tailwater condition.
If it is greater than half the pipe diameter. it is classified maximum condition.
Pipes that outlet onto wide flat areas with no defined channel are assumed
to have a minimum tailwater condition unless reliable flood stage elevations
shot- otherwise.
Outlet pipe diameter, Do (in.)
Tailwater depth (in.)
Minimum/Maximum tailwater?
Discharge (cfs)
Velocity (ft./s)
18
12
Max TW (Fig. 8.06b)
7.7
6.3
Step 2. Based on the tailwater conditions determined in step 1, enter Figure
8.06a or Figure 8.06b, and determine d50 riprap size and minimum apron length
(L). The d50 size is the median stone size in a well -graded riprap apron.
Step 3. Determine apron width at the pipe outlet, the apron shape, and the
apron width at the outlet end from the same figure used in Step 2.
Minimum TW Maximum TW
Figure 8.06a Figure 8.06b

Riprap d50, (ft.) 0.5 0.5
Minimum apron length, La (ft.) 10 10
Apron width at pipe outlet (ft.) 4.5 4.5
Apron shape
Apron width at outlet end (ft.) 11.5 5.5
Step 4. Determine the niaximiun stone diameter:
dMX= 1.5xd50
Minimum TW
Max Stone Diameter, dmax (ft.) 0.75
Step 5. Determine the apron thickness:
Apron Thickness(ft.)
Apron thickness = 1.5 x d...
Minimum TW
1.125
Maximum TW
0.75
Maximum TW
1.125
Step 6. Fit the riprap apron to the site by making it level for the miniiutun
length, Ld_ from Figure 8.06a or Figure 8.06b_ Extend the apron farther
dov.-nstream and along channel banks until stability is assured_ Keep the
apron as straight as possible and align it with the flogs- of the receiving stream.
Make any necessary alignment bends near the pipe outlet so that the entrance
into the receiving stream is straight.
Some locations may require lining of the entire channel cross section to assure
stability.
It may be necessary to increase the size of riprap where protection of the
channel side slopes is necessary (Appendix 8.05). NA -`here overfalls exist at
pipe outlets or flows are excessive, a plunge pool should be considered, see
page 8.06.8.